Low pressure refrigeration system with membrane purge

ABSTRACT

Disclosed is a refrigeration system including a heat transfer fluid circulation loop configured to allow a refrigerant to circulate through the circulation loop. A purge gas outlet is in operable communication with the heat transfer fluid circulation loop. The system also includes at least one gas permeable membrane having a first side in operable communication with the purge gas outlet and a second side. The membrane includes a separation layer including a porous inorganic material with pores of a size to allow passage of contaminants through the membrane and restrict passage of the through the membrane, and a polymer coating over the separation layer. A permeate outlet is in operable communication with the second side of the membrane.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Provisional Application62/584,073 filed Nov. 9, 2017, which is incorporated herein by referencein its entirety.

BACKGROUND

This disclosure relates generally to chiller systems used in airconditioning systems, and more particularly to a purge system forremoving contaminants from a refrigeration system.

Chiller systems such as those utilizing centrifugal compressors mayinclude sections that operate below atmospheric pressure. As a result,leaks in the chiller system may draw air into the system, contaminatingthe refrigerant. This contamination degrades the performance of thechiller system. To address this problem, existing low pressure chillersinclude a purge unit to remove contamination. Existing purge units use avapor compression cycle to separate non-condensable gas from therefrigerant. Existing purge units are complicated and lose refrigerantin the process of removing contamination.

BRIEF DESCRIPTION

Disclosed is a refrigeration system including a heat transfer fluidcirculation loop configured to allow a refrigerant to circulatetherethrough. A purge gas outlet is in operable communication with theheat transfer fluid circulation loop. The system also includes at leastone gas permeable membrane having a first side in operable communicationwith the purge gas outlet and a second side. The membrane includes aseparation layer including a porous inorganic material with pores of asize to allow passage of contaminants through the membrane and restrictpassage of the refrigerant through the membrane, and a polymer coatingover the separation layer. A permeate outlet is in operablecommunication with the second side of the membrane.

In some embodiments, the system further includes a prime mover operablycoupled to the permeate outlet, and the prime mover is configured tomove gas from the second side of the membrane to an exhaust port leadingoutside the fluid circulation loop.

In any one or combination of the foregoing embodiments, the heattransfer fluid circulation loop includes a compressor, a heat rejectionheat exchanger, an expansion device, and a heat absorption heatexchanger, connected together in order by conduit, and the purge gasoutlet is in operable communication with at least one of the heatrejection heat exchanger, the heat absorption heat exchanger, or themembrane.

In any one or combination of the foregoing embodiments, the systemfurther includes a retentate return conduit operably coupling the firstside of the membrane to the fluid circulation loop. In some embodiments,the prime mover is a vacuum pump.

In any one or combination of the foregoing embodiments, the systemfurther includes a purge gas collector operably coupled to the purgeoutlet and the membrane.

In some embodiments, the system further includes a prime mover operablycoupled to the permeate outlet, the prime mover configured to move gasfrom the second side of the membrane to an exhaust port leading outsidethe fluid circulation loop. In some embodiments, the prime moverincludes a vacuum pump in operable communication with the second side ofthe membrane.

In any one or combination of the foregoing embodiments, the systemfurther includes a filter in operable communication with the purgeoutlet and the first side of the membrane.

In any one or combination of the foregoing embodiments, the separationlayer includes a ceramic material.

In any one or combination of the foregoing embodiments, wherein themembrane includes zeolite.

In any one or combination of the foregoing embodiments, the at least onegas permeable membrane includes a plurality of gas permeable membranes;wherein the plurality of gas permeable membranes are arranged in serialor parallel communication.

In any one or combination of the foregoing embodiments, the polymerlayer includes a polymer selected from a silicone rubber, fluorosiliconeor polyimide.

In any one or combination of the foregoing embodiments, the polymerlayer has a thickness of 0.05 μm to 50 μm.

In any one or combination of the foregoing embodiments, the systemfurther includes a controller configured to operate the fluidcirculation loop in response to a cooling demand signal and to operatethe prime mover in response to a determination of contaminants in thefluid circulation loop.

In any one or combination of the foregoing embodiments, the controlleris configured to activate a purge back-flush mode in which gas istransported from the second side of the membrane to the first side ofthe membrane.

In any one or combination of the foregoing embodiments, the controlleris configured to activate a heat source to heat the membrane to atemperature to remove contaminants.

Also disclosed is a method of operating a refrigeration system,comprising circulating a refrigerant through a heat transfer fluidcirculation loop in response to a cooling demand signal. Purge gascomprising contaminants is collected from a purge outlet in the fluidcirculation loop. The contaminants are transferred across a permeablemolecular sieve membrane with a prime mover, said membrane comprising aporous inorganic or metal organic framework with pores of a size toallow passage of the contaminants through the membrane and restrictpassage of the refrigerant through the membrane. The method alsoincludes periodically back-flushing flushing the membrane bytransporting gas from the second side of the membrane to the first sideof the membrane, or periodically heating the membrane to a temperatureto remove contaminants, or both periodically transporting gas from thesecond side of the membrane to the first side of the membrane andperiodically heating the membrane to a temperature to removecontaminants.

In any one or combination of the foregoing embodiments, the methodincludes periodically back-flushing the membrane by transporting gasfrom the second side of the membrane to the first side of the membrane.

In any one or combination of the foregoing embodiments, the method alsoincludes periodically heating the membrane to a temperature to removecontaminants.

In any one or combination of the foregoing embodiments, the method alsoincludes passing the purge gas through a filter before reaching themembrane.

In any one or combination of the foregoing embodiments, the method alsoincludes transporting the contaminants through a polymer coating on theinorganic or metal organic framework membrane.

In any one or combination of the foregoing embodiments, the method alsoincludes collecting the purge gas in a purge gas collector between thepurge outlet and the membrane.

In any one or combination of the foregoing embodiments, the method alsoincludes returning refrigerant from the first side of the membrane tothe fluid circulation loop.

BRIEF DESCRIPTION OF THE DRAWINGS

The following descriptions should not be considered limiting in any way.With reference to the accompanying drawings, like elements are numberedalike:

FIG. 1 is a schematic depiction of a refrigeration system including avapor compression heat transfer refrigerant fluid circulation loop;

FIG. 2 is a schematic depiction of an example embodiment of a membranepurge system for a refrigeration system;

FIG. 3 is a schematic depiction of a separation membrane;

FIG. 4 is a schematic depiction of an example embodiment of a membranepurge system with purge collector and relevant components of a vaporcompression heat transfer refrigerant fluid circulation loop; and

FIG. 5 is a schematic depiction of another example embodiment of amembrane purge system with purge collector and relevant components of avapor compression heat transfer refrigerant fluid circulation loop.

DETAILED DESCRIPTION

A detailed description of one or more embodiments of the disclosedapparatus and method are presented herein by way of exemplification andnot limitation with reference to the Figures.

With reference to FIG. 1, a heat transfer fluid circulation loop such ascan be used in a chiller is shown in block diagram form in FIG. 1. Asshown in FIG. 1, a compressor 10 pressurizes heat transfer fluid in itsgaseous state, which both heats the fluid and provides pressure tocirculate it throughout the system. In some embodiments, the heattransfer fluid, or refrigerant, comprises an organic compound. In someembodiments, the refrigerant comprises a hydrocarbon or substitutedhydrocarbon. In some embodiments, the refrigerant comprises ahalogen-substituted hydrocarbon. In some embodiments, the refrigerantcomprises a fluoro-substituted or chloro-fluoro-substituted hydrocarbon.The hot pressurized gaseous heat transfer fluid exiting from thecompressor 10 flows through conduit 15 to heat exchanger condenser 20,which functions as a heat exchanger to transfer heat from the heattransfer fluid to the surrounding environment, resulting in condensationof the hot gaseous heat transfer fluid to a pressurized moderatetemperature liquid. The liquid heat transfer fluid exiting from thecondenser 20 flows through conduit 25 to expansion valve 30, where thepressure is reduced. The reduced pressure liquid heat transfer fluidexiting the expansion valve 30 flows through conduit 35 to heatexchanger evaporator 40, which functions as a heat exchanger to absorbheat from the surrounding environment and boil the heat transfer fluid.Gaseous heat transfer fluid exiting the evaporator 40 flows throughconduit 45 to the compressor 10, thus completing the heat transfer fluidloop. The heat transfer system has the effect of transferring heat fromthe environment surrounding the evaporator 40 to the environmentsurrounding the condenser 20. The thermodynamic properties of the heattransfer fluid must allow it to reach a high enough temperature whencompressed so that it is greater than the environment surrounding thecondenser 20, allowing heat to be transferred to the surroundingenvironment. The thermodynamic properties of the heat transfer fluidmust also have a boiling point at its post-expansion pressure thatallows the temperature surrounding the evaporator 40 to provide heat tovaporize the liquid heat transfer fluid.

With reference now to FIG. 2, there is shown an example embodiment of apurge system that can be connected to a vapor compression heat transferfluid circulation loop such as FIG. 1. As shown in FIG. 2, the purgesystem receives gas comprising refrigerant gas and contaminants (e.g.,nitrogen, oxygen, water vapor) through a connection 52 to a membraneseparator 54 on a first side of a membrane 56. A prime mover such as avacuum pump 58 connected to the membrane separator 54 through connection60 provides a driving force to pass the contaminants through themembrane 56 and exit the system from a second side of the membrane 56through an outlet 62. In some embodiments, the prime mover can be in thefluid loop, e.g., a refrigerant pump or compressor. Refrigerant gasremains on the first side of the membrane 56 and can return to the fluidcirculation loop through connection 64.

The membrane 56 comprises a porous inorganic material. Examples ofporous inorganic materials can include ceramics such as metal oxides ormetal silicates, more specifically aluminosilicates (e.g., ChabaziteFramework (CHA) zeolite, Linde type A (LTA) zeolite, porous carbon,porous glass, clays (e.g., Montmorillonite, Halloysite). Porousinorganic materials can also include porous metals such as platinum andnickel. Hybrid inorganic-organic materials such as a metal organicframework (MOF) can also be used. Other materials can be present in themembrane such as a carrier in which a microporous material can bedispersed, which can be included for structural or processconsiderations.

Metal organic framework materials comprise metal ions or clusters ofmetal ions coordinated to organic ligands to form one-, two- orthree-dimensional structures. A metal-organic framework can becharacterized as a coordination network with organic ligands containingvoids. The coordination network can be characterized as a coordinationcompound extending, through repeating coordination entities, in onedimension, but with cross-links between two or more individual chains,loops, or spiro-links, or a coordination compound extending throughrepeating coordination entities in two or three dimensions. Coordinationcompounds can include coordination polymers with repeating coordinationentities extending in one, two, or three dimensions. Examples of organicligands include, but are not limited to, bidentate carboxylates (e.g.,oxalic acid, succinic acid, phthalic acid isomers, etc.), tridentatecarboxylates (e.g., citric acid, trimesic acid), azoles (e.g.,1,2,3-triazole), as well as other known organic ligands. A wide varietyof metals can be included in a metal organic framework. Examples ofspecific metal organic framework materials include but are not limitedto zeolitic imidazole framework (ZIF), HKUST-1.

In some embodiments, pore sizes can be characterized by a pore sizedistribution with an average pore size from 2.5 Å to 10.0 Å, and a poresize distribution of at least 0.1 Å. In some embodiments, the averagepore size for the porous material can be in a range with a lower end of2.5 Å to 4.0 Å and an upper end of 2.6 Å to 10.0 Å. Å. In someembodiments, the average pore size can be in a range having a lower endof 2.5 Å, 3.0 Å, 3.5 Å, and an upper end of 3.5 Å, 5.0 Å, or 6.0 Å.These range endpoints can be independently combined to form a number ofdifferent ranges, and all ranges for each possible combination of rangeendpoints are hereby disclosed. Porosity of the material can be in arange having a lower end of 5%, 10%, or 15%, and an upper end of 85%,90%, or 95% (percentages by volume). These range endpoints can beindependently combined to form a number of different ranges, and allranges for each possible combination of range endpoints are herebydisclosed.

The above microporous materials can be can be synthesized byhydrothermal or solvothermal techniques (e.g., sol-gel,) where crystalsare slowly grown from a solution. Templating for the microstructure canbe provided by a secondary building unit (SBU) and the organic ligands.Alternate synthesis techniques are also available, such as physicalvapor deposition or chemical vapor deposition, in which metal oxideprecursor layers are deposited, either as a primary microporousmaterial, or as a precursor to an MOF structure formed by exposure ofthe precursor layers to sublimed ligand molecules to impart a phasetransformation to an MOF crystal lattice.

In some embodiments, the above-described inorganic or MOF membranematerials can provide a technical effect of promoting separation ofcontaminants (e.g., nitrogen, oxygen, or water molecules) fromrefrigerant gas, and low refrigerant loss. Other membrane materials,such as porous and non-porous polymers can be subject to solventinteraction with the matrix material, which can interfere with effectiveseparation. In some embodiments, the capabilities of the materialsdescribed herein can provide a technical effect of promoting theimplementation of various example embodiments of refrigeration systemswith purge, as described in more detail with reference to the exampleembodiments below. For example, non-porous polymers are typically usedas membranes in air separation, operating on a mechanism known as“solution-diffusion”, whereby molecules are separated by firstdissolving into the polymer matrix and then diffusing at different ratesacross the membrane layer. In most instances, separation is accomplishedbased on differences in the size of the molecules. However, whilerefrigerant molecules are much larger than non-condensable air and watervapor molecules, they have been found to have very high solubility intosuch polymer films, which results in lower separation factors thananticipated based on molecular size.

As mentioned above, the microporous molecular sieve material can bedisposed on a gas permeable inorganic porous support such as alumina orzirconia, or other porous ceramic or metallic (e.g., Fe, Ni) material.Thickness of the support can range from 10 μm to 10 mm, morespecifically from 100 nm to 750 nm, and even more specifically from 250nm to 500 nm. In the case of tubular membranes 70 as described in FIG.3, fiber diameters can range from 0.1 mm to 100 mm, and fiber lengthscan range from 0.02 m to 2 m.

In some embodiments, the microporous material can be deposited on thesupport as particles in a powder or dispersed in a liquid carrier usingvarious techniques such as spray coating, dip coating, solution casting,etc. The dispersion can contain various additives, such as dispersingaids, rheology modifiers, etc. Polymeric additives can be used; however,a polymer binder is not needed, although a polymer binder can beincluded and in some embodiments is included. However, a polymer binderpresent in an amount sufficient to form a contiguous polymer phase canprovide passageways in the membrane for larger molecules to bypass themolecular sieve particles. Accordingly, in some embodiments a polymerbinder is excluded. In other embodiments, a polymer binder can bepresent in an amount below that needed to form a contiguous polymerphase, such as embodiments in which the membrane is in series with othermembranes that may be more restrictive. In some embodiments, particlesof the microporous material (e.g., particles with effective diameter of0.01 μm to 10 mm, or in some embodiments from 0.5 μm to 10 μm, can beapplied as a powder or dispersed in a liquid carrier (e.g., an organicsolvent or aqueous liquid carrier) and coated onto the support followedby removal of the liquid. In some embodiments, the application of solidparticles of microporous material from a liquid composition to thesupport surface can be assisted by application of a pressuredifferential across the support. For example a vacuum can be appliedfrom the opposite side of the support as the liquid compositioncomprising the solid microporous particles to assist in application ofthe solid particles to the surface of the support.

In some exemplary embodiments, the layer is applied with a vacuumenhanced dip coating process where a surface of the support is contactedwith a liquid dispersion of the microporous material dispersion while avacuum is applied from the opposite side of the support (or in the caseof hollow tube membrane configuration of FIG. 3, the tubular support 72can be immersed in the liquid except for the open ends). The vacuum willdraw solvent from the dispersion through the porous support, resultingin deposition of the microporous particles onto the support. In the caseof hollow fiber membranes as shown in FIG. 3, this vacuum filtrationtechnique can be particularly effective, as the hollow core 76 providesan enclosed space from which to draw a vacuum without the necessity of avacuum frame or similar structure that would be needed for a flat orplanar membrane configuration.

After coating a layer of microporous particles onto the support, thelayer can be dried to remove residual solvent and optionally heated tofuse the microporous particles together into a contiguous layer.Exemplary heating conditions can be in a range having at temperatures ofat least 50° C., 75° C., or 100° C., more specifically from 20° C. to75° C., and even more specifically from 20° C. to 50° C.

Various membrane structure configurations can be utilized, including butnot limited to, flat or planar configurations, tubular configurations,or spiral configurations. An example embodiment of a tubularconfiguration is schematically depicted in FIG. 3. As shown in FIG. 3, atubular membrane 70 comprises a porous support configured as tubularshell 72 surrounded by a molecular sieve layer 74. Thickness of themolecular sieve layer can range from 2 nm to 500 nm, more specificallyfrom 2 nm to 100 nm, and even more specifically from 2 nm to 50 nm. Theshell 72 defines a hollow core 76 that is open at both ends. In someembodiments, multiple tubular membranes are disposed together in a tubebank with a header (not shown) at each end in fluid communication withthe hollow cores 76. In use, purge gas comprising refrigerant gas andcontaminants is delivered to the exterior of the membrane 70 at agreater pressure than that inside the hollow cores 76 (e.g., by drawinga vacuum on the hollow cores 76 through the headers). This pressuredifferential provides a driving force for non-condensable nitrogen,oxygen or water molecules to pass through the molecular sieve layerwhile the larger refrigerant molecules are restricted from passagethrough the molecular sieve layer 74.

In some embodiments, the microporous material can be configured asnanoplatelets such as zeolite nanosheets. Zeolite nanosheet particlescan have thicknesses ranging from 2 to 50 nm, more specifically 2 to 20nm, and even more specifically from 2 nm to 10 nm. The mean diameter ofthe nanosheets can range from 50 nm to 5000 nm, more specifically from100 nm to 2500 nm, and even more specifically from 100 nm to 1000 nm.Mean diameter of an irregularly-shaped tabular particle can bedetermined by calculating the diameter of a circular-shaped tabularparticle having the same surface area in the x-y direction (i.e., alongthe tabular planar surface) as the irregularly-shaped particle. Zeolitesuch as zeolite nanosheets can be formed from any of various zeolitestructures, including but not limited to, framework type MFI, MWW, FER,LTA, FAU, and mixtures of the preceding with each other or with otherzeolite structures. In a more specific group of exemplary embodiments,the zeolite such as zeolite nanosheets can comprise zeolite structuresselected from MFI, MWW, FER, LTA framework type. Zeolite nanosheets canbe prepared using known techniques such as exfoliation of zeolitecrystal structure precursors. For example, MFI and MWW zeolitenanosheets can be prepared by sonicating the layered precursors(multilamellar silicalite-1 and ITQ-1, respectively) in solvent. Priorto sonication, the zeolite layers can optionally be swollen, for examplewith a combination of base and surfactant, and/or melt-blending withpolystyrene. The zeolite layered precursors are typically prepared usingconventional techniques for preparation of microporous materials such assol-gel methods.

With reference again to FIG. 3, a polymer coating 78 is disposed overthe molecular sieve layer 74. The polymer can be virtually any type ofpolymer that is resistant to erosion by the refrigerant as a solvent andis capable of being coated onto the molecular sieve layer, including butnot limited to silicone polymers (i.e., polysiloxanes), fluorosilicones,or polyimides. The polymer coating can be applied by any techniqueincluding but not limited to spray coating, dip coating, roll coating,or extrusion, followed by curing of the polymer coating. In someembodiments, the polymer coating 78 can be permeable to both refrigerantgas and the contaminants, through either or both of porosity sieving orpolymer solvent effects. In some embodiments, the polymer coating 78 canallow for passage of both types of gases via a solution-diffusionmechanism. In some embodiments, the polymer coating can have a thicknessin a range with a lower end of 0.05 μm, 0.1 μm, 0.5 μm, and an upper endof 4 μm, 10 μm, or 50 μm. These range endpoints can be independentlycombined to form a number of different ranges, and all ranges for eachpossible combination of range endpoints are hereby disclosed. In someembodiments, the polymer coating can provide a technical effect ofprotecting the molecular sieve layer 74 from exposure to contaminantssuch as oils, or to physical damage. In some embodiments, the polymercoating can provide a technical effect of reducing leakage ofrefrigerant across the membrane through pinholes. Although the polymercoating may not be impervious to refrigerant molecules, it can fill inany pinholes and significantly reduce the rate of mass transfer throughany such pinholes. The inorganic layer 74 may also contain grainboundaries, through which larger refrigerant molecules can pass, whichreduces the layer's selectivity. The polymer coating can mask such grainboundaries, thereby reducing refrigerant permeance through the membrane.

With reference now to FIG. 4, another purge system is shown along withselected components of the refrigerant fluid circulation loop of FIG. 1.As shown in FIG. 4, a purge collector 66 receives gas vented from thecondenser 20. In some embodiments, the connection of the vent line tothe condenser can be made at a high point of the condenser structure. Insome embodiments, the purge collector can provide a technical effect ofpromoting higher concentrations of contaminants at the membrane, whichcan promote more effective mass transfer and separation. This effect canoccur through a stratification of gas in the purge collector in whichlighter contaminants concentrate toward the top of the purge collectorand heavier refrigerant gas concentrates toward the bottom of the purgecollector. In some embodiments, the purge collector 66 can be any kindof vessel or chamber with a volume or cross-sectional open space toprovide for collection of purge gas and for a low gas velocity duringoperation of the purge system vacuum pump 58 to promote stratification.Stratification can also occur at any time when the purge system is notoperating (including during operation of the refrigeration system fluidcirculation loop), as the purge collector 66 remains in fluidcommunication with the condenser vent line with essentially stagnant gasin the purge collector. Other embodiments can also be employed topromote higher concentrations of contaminants at the membrane separator54, as discussed in more detail below.

In some embodiments, refrigerant from the first side of membrane 56 canbe returned to the refrigerant fluid circulation loop. As shown in FIG.4, a connection 67 returns retentate gas from the first side of membrane56 to the refrigerant fluid circulation loop at the evaporator 40,through a control device such as expansion valve 68 utilized toaccommodate the pressure differential between the first side of themembrane 56 (which is close to the pressure at the condenser 20) andpressure at the evaporator 40. It should be noted that the controldevice can control either or both flow through or pressure drop acrossthe control device, and expansion valve 68 is shown as an integratedcontrol device unit that performs both functions for ease ofillustration, but could be separate components such as a control valveand an expansion orifice. In some embodiments, utilization of a bypassrefrigerant return can provide a technical effect of promoting greaterconcentrations of contaminants at the first side of membrane 56 byremoving gas at the membrane 56 that is concentrated with refrigerantafter removal of contaminant gas molecules through the membrane 56, sothat refrigerant-concentrated gas can be displaced with gas from thepurge collector 66 that has a higher concentration of contaminants. Theconnection 67 can also include a control or shut-off valve, which can beintegrated with an expansion device (i.e., an expansion valve), asdescribed in more detail in U.S. patent application Ser. No. 62/584,012,the disclosure of which is incorporated herein by reference in itsentirety. In alternative embodiments (not shown), the bypass conduit 67can return refrigerant-laden gas to a colder side of the condenser 20 orinlet of the compressor 10, in which case an expansion device may not beneeded due to lower pressure differential compared to that of a bypassreturn to the evaporator 40. In such as case, the connection 67 canutilize a control device such as a control or shut-off valve 68 thatdoes not provide gas expansion. Other system variations such ascentrifugal separators or chilling coils integrated with a purgechamber, pumped recycle of permeate back to the retentate (upstream)side of the membrane, cascaded multiple membranes, or alternative primemovers such as a thermal prime mover or a pump or compressor in thefluid circulation loop, are described in more detail in U.S. patentapplication Ser. No. 15/808,837, entitled “Refrigeration Purge System”,filed on Nov. 9, 2017, the disclosure of which is incorporated herein byreference in its entirety.

Additional embodiments can also be employed to protect or promotedurability of the membrane. For example, in some embodiments acontroller (not shown) in operative communication with various sensingand control components of the system can be configured to periodicallyactivate a purge backflush in which gas is transported from the second(i.e., permeate) side of the membrane to the first (i.e., retentate)side of the membrane. As used herein, “periodically” means thatactivation can be based on any sort of criteria including human operatoractivation, or predetermined criteria including but not limited to thepassage of time, accumulated system operating time, accumulated systempurge cycle time, or measured system criteria such as measured pressuredifferential across the membrane during purge cycle operation of theprime mover. The backflush mode can be activated by isolating themembrane separator 54 from the purge collector 66 and reversing thedirection of the driving force. For example, in the example embodimentsof FIGS. 4-5, this can be accomplished by switching a 3-way valve (notshown) in the conduit between the purge collector 66 and the membraneseparator 54 to simultaneously connect a bypass line (not shown) fromthe three-way valve connecting the suction side of the vacuum pump 58and the first side of the membrane 56 while isolating the first side ofthe membrane 56 from the purge collector 66. A similar 3-way valveconnection can be employed at the suction side of the vacuum pump 58 toredirect the vacuum pump connection between the second side of themembrane 56 or to the bypass line to the first side of the membrane 56.In some embodiments, the controller can be configured to periodicallyexpose the membrane 56 to heat to remove contaminants such as oil. Insome embodiments, the membrane can be heated to at least 200° C., or toat least 300° C., or to at least 400° C. Heating can generally be keptunder 200° C. in order to prevent degradation of the polymer layer 78,save energy and simplify thermal management.

In some embodiments, durability and protection of the membrane 56 can bepromoted by a filter such as a coalescing filter, moisture filter, orparticulate filter between the purge outlet and the membrane 56. In theexample embodiment shown in FIG. 5, a coalescing filter 79 is disposedin the gas flow path between the purge collector 66 and the membraneseparator 54. One type of coalescing filter can have a cylindrical innerrigid open mesh core (e.g., stainless steel) around which a fibercoalescing medium (e.g., borosilicate glass fiber) is disposed. In someembodiments, the coalescing medium can have a gradient pore structure byusing layers of increasing pore size. The inlet gas first encounters thesmallest pores, which increase with penetration distance to allow morespace as the coalesced droplets grow. The coalescing medium can besupported by an outer mesh structure to provide mechanical strengthwhich is then followed by a coarse outer wrap that serves as a drainagezone. Gas flows into the hollow core of the cylinder and then radiallyoutward through the filter media. Tiny liquid droplets are captured bythe inner filter media and coalesce into larger liquid droplets that arecaptured and removed in the radially outward drainage zone.

The term “about”, if used, is intended to include the degree of errorassociated with measurement of the particular quantity based upon theequipment available at the time of filing the application. For example,“about” can include a range of ±8% or 5%, or 2% of a given value.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the presentdisclosure. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,element components, and/or groups thereof.

While the present disclosure has been described with reference to anexemplary embodiment or embodiments, it will be understood by thoseskilled in the art that various changes may be made and equivalents maybe substituted for elements thereof without departing from the scope ofthe present disclosure. In addition, many modifications may be made toadapt a particular situation or material to the teachings of the presentdisclosure without departing from the essential scope thereof.Therefore, it is intended that the present disclosure not be limited tothe particular embodiment disclosed as the best mode contemplated forcarrying out this present disclosure, but that the present disclosurewill include all embodiments falling within the scope of the claims.

1. A refrigeration system comprising a heat transfer fluid circulation loop configured to allow a refrigerant to circulate therethrough; a purge gas outlet in operable communication with the heat transfer fluid circulation loop; at least one gas permeable membrane having a first side in operable communication with the purge gas outlet and a second side, said membrane comprising a separation layer comprising a porous inorganic material with pores of a size to allow passage of contaminants through the membrane and restrict passage of the refrigerant through the membrane, and a polymer coating over said separation layer; and a permeate outlet in operable communication with the second side of the membrane.
 2. The refrigeration system of claim 1, further comprising a prime mover operably coupled to the permeate outlet, the prime mover configured to move gas from the second side of the membrane to an exhaust port leading outside the fluid circulation loop.
 3. The refrigeration system of claim 1, wherein the heat transfer fluid circulation loop comprises a compressor, a heat rejection heat exchanger, an expansion device, and a heat absorption heat exchanger, connected together in order by conduit; wherein the purge gas outlet is in operable communication with at least one of the heat rejection heat exchanger, the heat absorption heat exchanger, or the membrane.
 4. The refrigeration system of claim 2 wherein the prime mover comprises a vacuum pump in operable communication with the second side of the membrane.
 5. The refrigeration system of claim 1, further comprising a filter in operable communication with the purge outlet and the first side of the membrane.
 6. The refrigeration system of claim 1, wherein the separation layer comprises a ceramic material.
 7. The refrigeration system of claim 6, wherein the membrane comprises zeolite.
 8. The refrigeration system of claim 1, wherein the at least one gas permeable membrane comprises a plurality of gas permeable membranes; wherein the plurality of gas permeable membranes are arranged in serial or parallel communication.
 9. The refrigeration system of claim 1, wherein the polymer layer comprises a polymer selected from a silicone rubber, fluorosilicone or polyimide.
 10. The refrigeration system of claim 1, wherein the polymer layer has a thickness of 0.05 μm to 50 μm.
 11. The refrigeration system of claim 1, further comprising a controller configured to operate the fluid circulation loop in response to a cooling demand signal and to operate the prime mover in response to a determination of contaminants in the fluid circulation loop.
 12. The refrigeration system of claim 11, wherein the controller is configured to activate a purge back-flush mode in which gas is transported from the second side of the membrane to the first side of the membrane.
 13. The refrigeration system of claim 11, wherein the controller is configured to activate a heat source to heat the membrane to a temperature to remove contaminants.
 14. A method of operating a refrigeration system, comprising circulating a refrigerant through a heat transfer fluid circulation loop in response to a cooling demand signal; collecting purge gas comprising contaminants from a purge outlet in the fluid circulation loop; transferring the contaminants across a permeable molecular sieve membrane with a prime mover, said membrane comprising a porous inorganic or metal organic framework with pores of a size to allow passage of the contaminants through the membrane and restrict passage of the refrigerant through the membrane; and periodically back-flushing the membrane by transporting gas from the second side of the membrane to the first side of the membrane, or periodically heating the membrane to a temperature to remove contaminants, or both periodically transporting gas from the second side of the membrane to the first side of the membrane and periodically heating the membrane to a temperature to remove contaminants.
 15. The method of claim 14, comprising periodically back-flushing the membrane by transporting gas from the second side of the membrane to the first side of the membrane.
 16. The method of claim 14 comprising periodically heating the membrane to a temperature to remove contaminants.
 17. The method of claim 14, further comprising passing the purge gas through a filter before reaching the membrane.
 18. The method of claim 14, further comprising transporting the contaminants through a polymer coating on the inorganic or metal organic framework membrane.
 19. The method of claim 14, further comprising collecting the purge gas in a purge gas collector between the purge outlet and the membrane.
 20. The method of claim 14, further comprising returning refrigerant from the first side of the membrane to the fluid circulation loop. 